1. Field of the Invention
The present invention relates to a binocular magnifier which is mainly used by a weak-sighted person to obtain excellent binocular vision.
2. Description of the Related Art
Glasses and magnifiers for weak-sighted persons which have lenses for correcting weak eyesight impart an effective viewing function to weak-sighted persons who can read relatively large letters or the like but cannot read relatively small letters or the like.
Such glasses for weak-sighted persons include monocular and binocular types, and in order to obtain a high magnifying power it is general practice to employ telescope type glasses that utilize a combination of two or more lenses.
The conventional binocular glasses for weak-sighted persons suffer, however, from various problems such as a narrow field of view, a short working distance, a heavy weight due to the structure in which two or more lenses are combined together in one unit using a lens tube, and an inferior appearance in use. Further, since glasses for weak-sighted persons require an eye examination for each individual user, orders therefor cannot readily be fulfilled. For these reasons, magnifiers are generally employed to obtain magnified images with ease. Magnifiers provide a relatively wide field of view and a sufficiently long working distance. However, when binocular vision is effected using a single magnifier, various problems are experienced. More specifically, since the right and left eyes have different fields of view inside the lens and since the fields of view inside and outside the lens of the right and left eyes overlap each other, the visual axes oscillate, so that the process of obtaining a fusion image by convergence and accommodation which constitute the binocular vision function becomes considerably unstable.
Vergence is the function to concentrate the visual axes of the right and left eyes on an object by turning the eyes inwardly.
Accommodation is the function to form the image of an object on the retina by varying the curvature of each crystalline lens in accordance with the distance between the retina and the object.
Fusion is the phenomenon that visual impressions on the retinae of the right and left eyes are superposed one upon the other by the eye movement to thereby form one impression.
Accordingly, employment of a magnifier for binocular vision forces the user to make considerable efforts, and it is therefore difficult to use a magnifier for a long period of time.